Selection of Fan Equipment
Fans should be selected with the following recommended features to ensure good
quality, top performance, and long life (pertains to propeller-type fans):
- Direct-drive fans should have cast airfoil shaped propellers or
welded propellers which are balanced to minimize vibration.
-
Belt-drive fans should be cast airfoil blades or heavier airfoil shaped
blades formed from sheet steel, welded to the hub, and balanced.
-
Bearing on the fan shaft should be permanently lubricated and
sealed ball bearings in a self-aligning mount.
-
Fan frames should have a deep curved orifice at the blade tips for
smooth air flow and increased efficiency.
-
Tip clearance should be within 1/8- to 1/4-inch for efficiency under
static pressure.
-
Fan blade should be positioned in the orifice or venturi ring and not
behind it.
-
Fan motors should be: totally enclosed, ball bearing and thermally
protected.
-
Shutters should have smooth operating blades, be tie-rod
connected, have bronze or nylon pivot bearings, have a sturdy
frame and blades, and be as large as the fan.
-
Fans which are mounted to operate against wind movement (wall
mounted blowing out) should have 1/8-inch AMCA rating.
-
Weather hoods may be necessary to prevent wind, rain, and snow
from blowing directly into or through the fan and shutter
installation.
Section Break (Next Page)
Fan Horsepower
Fans must be sized based upon volume of air delivery and static pressure. Fan motors
must be sized on the same criteria as fans. The expression below gives the fan motor
horsepower required if it is assumed that most fans are about 50 percent efficient in
moving air. The constant 3178 is a conversion factor. Static pressure is usually about 1/8
inch static pressure.
Fan hp. = cfm x static pressure in inches of water
3178
If air flow is 25,000 CFM and the pressure is 1/8 inch of water the
fan hp is as follows:
Fan hp. = 25,000 X 0.125 = 0.98 or 1 hp.
3178
Table E3.1: Typical ventilation rates for poultry and livestock in closed, insulated buildings
Animals or
Birds Housed
At Minimum
Cold Temperature
At Average
Jan. Temperature
Summer
Minimum
Cubic Feet Per Minute (CFM) Per Bird or Animal
Layers (Light)
Layers (Heavy)
Broilers
Pullets
Turkeys, Breeders
Turkey, Hens
Turkey, Toms
Sow and Litter
Hog @ 200 lbs.
Hogs @ 50 lbs.
Dairy Cow @ 1000 lbs.
Dairy Calf @ 100 lbs.
Beef Animal @ 100 lbs.
Beef Calf @ 100 lbs.
Sheep @ 200 lbs.
1/4
1/3
1/10
1/10
3/4
1/2
1/2
10
5
1
1/2
2/3
1/4
1/4
2
1-1/2
2
30
20
5
20
5
50
10
25
5
*Or at least one air change per minute.
50
10
5
5
6
8
5
5
25
20
25
500
50
25
600
100
500
100
25